Contact High: Lenses That Deliver Drugs

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Contact High: Lenses That Deliver Drugs

Dry-eye sufferers and glaucoma patients may soon be able to trade their messy eye drops for a contact lens that delivers medication gradually over time.

Although eye drops account for 90 percent of all eye medication, drops are irritating and inefficient. Doctors estimate that only 1 to 7 percent of the medication actually gets absorbed into the eye, while the rest drips down the cheeks or into the back of the throat.

Even worse, many patients hate eye drops or forget to take them. For example, up to 59 percent of glaucoma patients regularly skip their drops, even though untreated glaucoma can lead to blindness.

Researchers have been working for nearly a decade on drug-dispensing contact lenses that could deliver eye medication more effectively, but they've struggled to design a lens that releases a continuous supply of the meds. Now, scientists report that they've created a contact lens that can deliver a high concentration of antibiotic at a constant rate for more than 30 days.

"The main way our lens differs is that it can provide large amounts of drug released at constant rates for long periods of time, which previous discoveries have not been able to do," said drug-delivery researcher Daniel Kohane of Harvard Medical School, who co-authored the paper published in the July issue of Investigative Ophthalmology & Visual Science. Past lenses have only been able to release a small amount of drug over a long period of time, or a substantial amount of drug for a day or two, he said.

Previous design attempts focused on dissolving medication into the hydrogel material that contacts are made of, or encasing a drug inside nanoparticles and then incorporating the particles into the hydrogel lens. The Boston researchers describe their new design like a pita pocket, with a big wad of drug in the middle of a hydrogel exterior.

"People had done all kinds of fancy things, but the problem with a lot of the methods was that the actual drug loading was very low," Kohane said. "It's not clear why no one did this before. It was very much like we invented the sandwich."

Because the drug-containing portion of the lens is shaped like a doughnut, it shouldn't affect the wearer's vision, he said.

To make their lens, the researchers took a biodegradable polymer called PLGA and dissolved it in an organic solvent, and then they added their drug. As the solvent evaporated, they were left with drug mixed into a polymer film. Finally, they coated the film in a hydrogel called pHEMA, which is the same material that's used to make regular contact lenses.

The group chose the PLGA polymer and the pHEMA hydrogel because both materials are FDA-approved for use in the eye. But the same technique could be used with different materials to adjust the speed of drug delivery. "Both the polymer film and pHEMA have some influence over slowing diffusion of the medication," said ophthalmologist Joseph Ciolino of the Massachusetts Eye and Ear Infirmary, a co-author on the study. "So we can change the rate of drug release depending on the ratio of polymer to drug, and depending on the molecular weight of the polymer we use."

Kohane and colleagues tested their prototype lens with an antibiotic called ciprofloxacin, which is commonly used to treat eye infections. In lab experiments, the contact lens released approximately 134 micrograms of drug each day for 30 days, enough to block bacterial growth for the duration of the study. "The rates of drug efflux that we got from these are vastly more than any other drug-eluting lens that we are familiar with," Kohane said.

So far, the group has only tested the diffusion properties of the lens in a lab dish. But they have high hopes for the future: "We're moving toward animal testing as we speak, and humans will be within a year or so," Kohane said. "It's just a matter of when we will be able to get lenses that are high-quality enough to use in a human eye."